The present invention relates to a digital television receiver and, more particularly, to a digital television signal processing circuit with improved hue correction of PAL signals.
Signal processing in a conventional television receiver is performed in an analog manner. However, there are problems with analog signal processing after image detection, such as poor luminance signal/chrominance signal separation (to be referred to as Y/C separation hereinafter) which appears as cross-color dots on a screen, poor image quality, and poor synchronization. These problems are caused by phase shifting among various signals along the time base, which is a common drawback with analog signal processing circuits. Meanwhile, when an integrated circuit is used, there is an increase in the number of external parts and portions to be adjusted. Therefore, the manufacturing process is more complicated, and the cost is increased.
In order to resolve these problems, video detection signals can be digitally processed after the video signals have been detected.
A PAL hue correction circuit using a 1-horizontal period (to be referred to as 1H hereinafter) delay line is installed in a television receiver of a
system. In a signal processing system of a transmission or a television receiver, the PAL hue correction circuit corrects hue distortions occurring in a video signal by a calculation using line correlation. More specifically, a chrominance signal of the PAL system is precisely separated into U and V signals using a comb filter. The comb filter comprises a 1H delay line and a calculator and can separate a chrominance signal having a frequency of f=(n.+-.1/4)fH (where fH is a horizontal scanning frequency) near a subcarrier frequency into a U signal having a frequency of f=(n-1/4)fH and a V signal having that of f=(n+1/4)fH. (where n is an indicated integer).
As described above, a television receiver of the PAL system is provided with a hue correction circuit. In addition, the television receiver is also provided with a Y/C separation circuit. Y/C separation circuits are classified into those which separate by using a normal band-pass filter and those which use a comb filter. The latter circuit is known to have superior performance. In the comb filter in the signal processing circuit of the PAL system, the chrominance signal has a frequency of f=(n.+-.1/4)fH. For this reason, if only one 1H delay line is used, it is difficult to perform Y/C separation. Thus, the comb filter is realized by using two 1H delay lines. When the comb filter of this type is used, cross-color interference can be reduced, thereby obtaining an image with high resolution.
As described above, in a television receiver of the PAL system, in order to improve performance, one 1H delay line for the hue correction circuit and two 1H delay lines for the Y/C separation circuit are required, that is, three 1H delay lines are needed. However, the 1H delay line is larger and more expensive than other components. Therefore, if three 1H delay lines are provided, the signal processing circuit becomes relatively expensive.